"I've Got Your Back"

Charles Darwin had more in common with chimpanzees than even he realized. Before he was universally known for his theory of natural selection, the young naturalist made a decision that has long been hailed as the type of behavior that fundamentally separates humans from other apes.

In 1858, before Darwin published On the Origin of Species, his friend Alfred Russel Wallace mailed Darwin his own theory of evolution that closely matched what Darwin had secretly been working on for more than two decades. Instead of racing to publish and ignoring Wallace’s work, Darwin included Wallace’s outline alongside his own abstract so that the two could be presented jointly before the Linnean Society the following month. “I would far rather burn my whole book than that [Wallace] or any man should think that I had behaved in a paltry spirit,” Darwin wrote.

This kind of prosocial behavior, a form of altruism that seeks to benefit others and promote cooperation, has now been found in chimps, the species that Darwin did more than any other human to connect us with. (This month's Science Agenda, about medical testing in chimps, notes other similarities that have been documented in chimps and humans.) In the study, published in the Proceedings of the National Academy of Sciences USA, primatologist Frans de Waal and his colleagues at the Yerkes National Primate Research Center at Emory University presented chimps with a simplified version of the choice that Darwin faced.

Pairs of chimps were brought into a testing room where they were separated only by a wire mesh. On one side was a bucket containing 30 tokens that the chimpanzee could give to an experimenter for a food reward. Half of the tokens were of one color that resulted in only the chimpanzee that gave the token receiving a reward. The other tokens were of a different color that resulted in both chimpanzees receiving a food reward. If chimpanzees were motivated only by selfish interests, they would be expected to choose a reward only for themselves (or it should be 50–50 if they were choosing randomly). But individuals were significantly more likely to choose the prosocial outcome compared with the no-partner control.

De Waal says that previous studies showing chimps to be selfish may have been poorly designed. “The chimps had to understand a complex food-delivery system,” De Waal wrote via e-mail, “and were often placed so far apart that they may not have realized how their actions benefited others.” De Waal added that his study does not rule out the possibility that chimpanzees were influenced by reciprocal exchanges outside the experimental setting such as grooming or social support.

This latter possibility offers exciting research opportunities for the future. Chimpanzee society, like the greater scientific community that studies them, is built around such reciprocal exchanges. Science is a social activity, and sharing the rewards from one another’s research allows scientists to improve their work over time. Like the chimpanzees he would bond us with, Darwin recognized the utility of sharing rewards with others. Behaving in a “paltry spirit” was not the proper choice for a cooperative ape.

Adapted from The Primate Diaries, part of Scientific American's blog network.